Plasma Impedance Tuning Effect on Nanostructure of Diamond Films

摘要

The morphology and structure of nanocrystalline diamond films as well as the plasma chemistry were studied by altering the plasma impedance. These impedances related to electron density were altered via the matching system. Two films were grown by the microwave plasma under different values of the plasma impedance, resulting in low and high electron densities in the plasma. By the use of measurements of plasma impedance and optical emission, the lowering of an inductive component of the impedance, indicating an increasing electron density, encouraged H-radical concentration present in the plasma. As the plasma was changed to the high electron density, Raman spectra of the films showed the sp~3 Raman peak shifted from 1325 to 1328.5 cm~(-1) with narrower broadening. This behavior arose from an increase in grain size, corresponding to images from a field emission scanning electron microscope. Raman spectra of G-peak position and white light reflectometry showed a reduction in sp~2 carbon content of the film. The G-peak shifted from 1564 to 1541 cm~(-1) and refractive index increased from 1.84 to 2.16. The formation of the films related to the concentrations of H and CH_3 radicals. The plasma impedance affected the radical concentrations.